VB treeview控件的问题

使用Treeview控件，有错误，请帮忙。Public Sub MakeTree(tvwX As TreeView)
 Dim nodX As Node
 Dim sNodeKey As String
 Dim sRelative As String
 Dim MsgText As String
 txtSQL = "select * from 系部"
 Set mrc = ExecuteSQL(txtSQL, MsgText)
 '添加系
 Do Until mrc.EOF
 sNodeKey = "X" & mrc("系部代码").Value
 Set nodX = tvwX.Nodes.Add(, , sNodeKey, mrc("系部名称").Value)
 nodX.Tag = "系"
 mrc.MoveNext
 Loop
 mrc.Close
 txtSQL = "select * from 专业"
 Set mrc = ExecuteSQL(txtSQL, MsgText)
 '添加专业
 Do Until mrc.EOF
 sNodeKey = "X" & mrc("专业代码").Value
 sRelative = Mid$(sNodeKey, 1, 3)
 Set nodX = tvwX.Nodes.Add(, , sNodeKey, mrc("专业名称").Value)
 nodX.Tag = "专业"
 mrc.MoveNext
 Loop
 mrc.Close
 txtSQL = "select * from 班级"
 Set mrc = ExecuteSQL(txtSQL, MsgText)
 '添加班级
 Do Until mrc.EOF
 sNodeKey = "X" & mrc("班号").Value
 sRelative = Mid$(sNodeKey, 1, 5)
 Set nodX = tvwX.Nodes.Add(, , sNodeKey, mrc("班级名称").Value)
 nodX.Tag = "班级"
 mrc.MoveNext
 Loop
 mrc.Close
 Set tvwX.SelectedItem = tvwX.Nodes(1)
 Set mrc = Nothing
 Set nodX = Nothing
 End Sub
 Private Sub Form_Load()
 Call comboAddItem(Combo2, "班级", 0)
 Call comboAddItem(Combo3, "系部", 0)
 Call MakeTree(TreeView1)
 End Sub
 代码是这样写的，可是显示的时候不分层啊，老是一下子全部显示出来了！请大家帮忙，